Test to measure curling tendency of paper in laser printers

ABSTRACT

The invention provides an apparatus and method for testing the tendency of a paper to curl. The paper is cut from a paper making machine and rapidly humidified to standard TAPPI conditions, and is thereafter run through an apparatus having a substantially vertically oriented nip. The paper is measured for curl, all data are tabulated and fed back into a data acquisition or paper machine control system.

FIELD OF THE INVENTION

The present invention relates to a testing instrument and method formeasuring the curling tendency of paper in laser printers, photocopiersor other like sheet-fed apparatuses.

BACKGROUND OF THE INVENTION

In a typical laser-based printing/copying process, a photoconductivemember is charged to a substantially uniform potential so as tosensitize the surface thereof. The charged portion of thephotoconductive member is exposed to a light image of the originaldocument being reproduced. Exposure of the charged photoconductivemember selectively dissipates the charges thereon in the irradiatedareas. This records a latent image on the photoconductive membercorresponding to the informational areas contained within the originaldocument.

One approach to the fixing of toner images onto a support has been topass the support bearing the toner images between a pair of opposedroller members, at least one of which is internally heated. Duringoperation of a fixing system of this type, the support member to whichthe toner images are electrostatically adhered is moved through the nipformed between the rolls and thereby heated under pressure. A largequantity of heat is applied to the toner and the copy sheet bearing thetoner image. This heat evaporates much of the moisture contained in thesheet. The quantity of heat applied to the front and to the back sidesof the sheet is often not equal.

One problem associated with moisture loss in paper is paper curl.Deformation of the paper generally occurs due to a change of physicalproperties in the z-direction of paper. This may occur through thefollowing event: as sheets pass through an image fixing system, moistureis driven out and the sheet temperature is elevated. After image fixing,a sheet typically rests in a collection area exposed to its ambientsurroundings, where its moisture content will reach equilibrium with theenvironment through absorption of moisture across the full face of atleast one side of the paper sheet. However, if the copy sheet becomespart of a large compiled set, both sides of all of the papers in thecompilation (except for the top sheet) will effectively be sealed offfrom ambient moisture. The only route available to the papers formoisture re-absorption is through the edges of the sheets, leaving themoisture content of the central portions of the sheets relativelyunchanged. This uneven pattern of moisture re-absorption results in edgestresses that lead to paper curl along the edges of the paper.

Further, contact with moisture can cause curl prior to image fixing.Thus, in addition to being cosmetically unsightly, the curl creates ahandling problem, in that pages with a wave pattern along their edgesare more difficult to feed to secondary paper handling machines. It isespecially important to papers which are used in automatic sheet-fedprinting operations such as xerography. Excessive curl can cause thepaper transport mechanism to jam, thereby creating operator frustration,lost time and service expense. Therefore, curl is an importantmechanical property of non-woven webs such as paper which manufacturersseek to minimize, and there is a continuing need for a measuring deviceto predict the curl performance of webs which will be used in sheet-fedmachines.

Moreover, in sheet-fed apparatuses, curl behavior is further influencedby the heat conductivity of the paper, moisture evaporation from thepaper, and the other heating conditions. Thus, curl behavior isinfluenced by different types of paper as well as different apparatusesused with the same type of paper, resulting in the generalunpredictability of the tendency of a paper to curl.

Generally, two types of curl may be generated in paper manufacture as aresult of moistening or drying a paper sheet. Total (simplex) curl iswhen a paper curls in one direction, such as a sheet of paper rolledinto a cylindrical tube. Diagonal curl results from a twist of paper,such that one portion of the paper rotates axially in one direction,while another portion of the paper rotates axially in a different,generally opposite direction.

Current curl tests for prediction of curl tendency are problematic. Oneprocedure involves running multiple sheets through a specified (Xerox5388) photo copier, hanging a preset number of sheets by the long edgeand matching the resulting bend to a pattern of curves on a referencetemplate. This test, however, requires the use of specific, expensiveequipment and is costly and time consuming. It also requires that papersbe sheeted prior to testing, delaying results.

Hot plate curl is another method currently in use. It involves placingcut samples on a heated hotplate and manually measuring the corners ofthe sample as they curl away from the heat. This method is timeintensive and has very poor (r^2 0.30) correlation to end use as well aspoor reproducibility.

Other tests do not account for the ability of gravity to alter the curlof a paper, resulting in errant data. For example, other mechanisms,such as a computer controlled hot-roll fusing apparatus, are able totest for a variety of paper parameters by mimicking the environment of atypical consumer printer, yet the nips are horizontal and have too highnip pressure, resulting in gravitational and mechanical effects on thetest samples.

Therefore, it is an object of this invention to provide a test for thetendency of a paper to curl from which information can be achievedquickly and possible corrective feedback is rapid, has a low level ofvariability, and accounts for the effect of gravity on a tendency tocurl for a variety of paper samples.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a method and apparatus fortesting the tendency of a paper to curl in sheet-fed apparatusescomprising moving test paper sheets from a paper making machine, rapidlyconditioning the paper sheets to a desired humidity, and moving thepaper sheets through a test nip similar to a nip of a sheet-fedapparatus. The nip is positioned substantially vertically so that thepaper is substantially vertically positioned when it exits the nip. As,or immediately after, the paper exits the nip, the paper is measured forcurl with a measuring means. Corrective curl information is calculatedfrom the curl measurement means, and the information can be relayed backinto a paper machine to aid the paper making process to correct for thetendency of a paper to curl.

According to the present invention, the preferred method for measuringthe tendency of a paper to curl involves the steps of moving a papersample from a paper making machine, moving the paper sample through asubstantially vertical nip positioned such that the paper sample exitsfrom the substantially vertical nip in a substantially verticalorientation, and measuring the diagonal curl of the paper sample as orafter the paper sample exits the substantially vertical nip.

Further embodiments of the invention include adjusting the temperaturein the nip such that a sample paper's temperature exiting the nip isbetween 50-350° F., adjusting the pressure so that the pressure in thenip is minimal, and adjusting the temperature of the nip from a range of150-450° F. Further, the humidity of the testing environment iscontrolled such that the sample paper is conditioned in thisenvironment. The measurements are captured by a computer, and finalsimplex printer curl is predicted by combining the diagonal curl of thepaper sample with the moisture content of the paper sample prior toconditioning in the controlled humidity environment in a regressionanalysis. Corrective information can be obtained from this data and fedback into the paper making machine control panel.

In other embodiments, the invention comprises an apparatus to implementthe above method having a nip of two substantially vertically mountedrollers monitored by a computer and located in proximity to a curlmeasuring means that measures the paper as, or after, it exits the nipin a substantially vertical orientation.

Other objects, embodiments, features and advantages of the presentinvention will be apparent when the description of a preferredembodiment of the invention is considered in conjunction with theannexed drawings, which should be construed in an illustrative and notlimiting sense.

BRIEF DESCRIPTION OF THE FIGURES/DRAWINGS

FIG. 1 is a partial top view of an apparatus for testing the tendency ofa paper to curl.

FIG. 2 is a partial side view of an apparatus for testing the tendencyof a paper to curl.

FIG. 3 a is a partial side view of one embodiment of a rapid conditionersystem.

FIG. 3 b is a partial front view of one embodiment of a rapidconditioner system.

FIG. 4 is a full perspective view of one embodiment of an apparatus fortesting the tendency of a paper to curl.

FIG. 5 is a chart showing a analysis of predicted simplex curl vs.actual simplex curl.

DETAILED DESCRIPTION

An apparatus 10 in accordance with one embodiment of the invention isshown in FIG. 1. Two substantially vertically oriented mounted rollers12 and 14 are aligned in parallel and close proximity creating a nippoint 16 between the rollers. Roller 12 is operably connected to acomputer, such that the computer can control the roller's speed,temperature and other variables. In one embodiment, the computer can beprogrammed to heat roller 12 to a preferred temperature range of 200 to275° F., although lighter paper grades may require temperature ranges aslow as 150° F. and heavier paper grades may require temperature rangesup to 450° F. Generally, the heating of roller 12 is achieved with aheat lamp 38 fixed along the substantially vertical axis of the roller.However, other heat devices may be used within the spirit of theinvention. Further, other non-computer controlled heat devices may beused if no computer is available or desired.

Substantially vertically mounted roller 14 is a spring mounted rollermounted in close proximity to substantially vertically mounted roller12. The spring pressure of roller 14 is zero or minimal and adjustedsuch that a paper that passes through nip 16 has zero mechanical curl.For the purposes of this application, the term mechanical curl shallmean the amount of curl a paper would have if the rollers defining thenip were unheated. The required spring pressure for roller 14 isadjusted with standard springs and/or spring preloads and can vary frommachine to machine, with the desired pressure being the maximum pressureachievable while still maintaining no mechanical curl. As a result,pressure within the nip is zero or minimal even as the rollers are inclose proximity. Roller 14 generally does not contain a heat lamp,although one may be included if desired. Further, roller 14 is notnecessarily controlled by the computer.

The rollers can be any type of rollers known in the art. Since paper isused in numerous types of apparatuses, other embodiments of theinvention test the tendency of the paper to curl where the paper isintended to be used in a variety of apparatuses. This can be achieved bycreating a substantially vertical nip that mimics the horizontal nip ofthe apparatus for which the test paper is intended. The presentembodiments, however, are directed to paper intended for a typicalxerographic machine, for example, a Xerox 5388 copier, and the relatedrollers and nips.

The rollers are rotated by a variable speed motor as directed by thecomputer. The speed can be altered to regulate the total contact time apaper has against the rollers as it passes through the nip, which inturn relates to the heat passed onto the paper in the nip, and the speedof the measuring operation.

The temperature of the rollers and the paper passing between the rollersare monitored by at least one heat sensor. In the embodiment depicted inFIG. 1, three heat sensors are utilized, wherein sensors 20, 22 and 24monitor the temperature of the paper, roller 12 and roller 14respectively. Sensor 20 monitors paper temperature as it leaves the nip.The temperature of the paper achieved during the testing process iscritical. If the paper falls below the minimum temperature range, thepaper will fail to achieve a heated plastic state that permits curltendency, if any, to dominate. Heat sensors 22 and 24 monitor theindividual rollers to maintain the nip at the desired temperature withinthe preferred temperature range of 200 to 275° F. When the paper passesthrough the nip point, a transfer of heat occurs between the roller andthe paper, thus heating the paper and slightly cooling the rollers. As aresult, rapid movement of a multiplicity of paper through the rollerscould result in the temperature of the rollers decreasing below thedesired range, adversely affecting test results. Temperature sensorsprompt a user to temporarily suspend operation when the temperature ofthe rollers drop, thereby allowing the heating mechanism time tore-stabilize the system. Alternatively, the sensors may be hooked into afeedback loop with the computer such that the computer can automaticallycorrect or compensate for the temperature if it threatens to fall toofar from the desired temperature.

In sheet-fed machines, paper is generally heated on one side only, andcurl behavior is influenced by the heat conductivity of paper, moistureevaporation from paper and the types of rollers or nips used. Thus, thetypes of nips, rollers, temperature range and speed can be adjusteddepending on the type of paper being tested and the type of instrumentwith which the paper is intended to be used.

A theoretical centerline 30 extends outwardly from the nip,perpendicular to rollers 12 and 14. Two standard laser sensors 26 and 28are positioned in parallel in a substantially vertical plane at adistance from the nip such that parallel lasers are emitted from the twosensors crossing centerline 30 along points 32. Points 32 are preferablyin close proximity to the nip point such that the paper can be measuredfor curl immediately after it leaves the nip. In the present embodiment,the distance between the nip and points 32 is about 37 mm. The exactdistance can vary by several mm. However, if points 32 is too close tothe nip point, no curl will be recorded by the lasers.

The distance between the lasers and the nip can vary as long as it iswithin the range of the sensors. The laser sensors emit laser beamstoward the paper as or immediately after it leaves the nip, and curl ismeasured regardless of which direction the paper curls. For example, ifthe paper curls toward heated roller 12, the laser sensors report apositive value. Conversely, if the paper curls toward the pressureroller 14, a negative value is obtained. Alternatively, if the paperdoes not curl, calculations will reveal a zero value.

Feed slot 58 is located in operable connection with rollers 14 and 16.Testing paper is loaded into the feed slot, and in turn is fed into thenip point. The feed slot can take the form of any device known in theart that can hold and feed paper into a nip point. The feeder designmust not inhibit or promote curl.

FIG. 2 depicts an alternate view of the embodiment. Laser sensors 26 and28 emit lasers toward the centerline that are parallel to each other, indifferent horizontal planes, and perpendicular to centerline 30. Theyare preferably about 3-5 inches apart in the substantially verticalplane. However, the exact distance can vary within the spirit of theinvention. Further, in FIG. 2, the mounting devices of the rollers arepictured. Pressure roller 16 is mounted on pressure bearing springs 34.Drive gear 36 is operably connected to roller 12 and is furtherconnected to a motor 52 or other mechanical device that engages thedrive gear. When the motor is activated, the drive gear is rotated,which in turn rotates roller 12.

The preferred embodiment of the method for measuring the tendency of apaper to curl involves moving a paper sample from a standard papermaking machine to the apparatus above, and then moving the paper samplethrough the substantially vertical nip positioned such that the papersample exits from the substantially vertical nip in a substantiallyvertical orientation, and then measuring the diagonal curl of the papersample as or after the paper sample exits the substantially verticalnip. The paper samples may be moved from the paper making machine in anautomated in-line process or they may be physically carried from thepaper making machine to the substantially vertical nip of FIGS. 1-2.

Further embodiments of the method involve humidifying the paper samplesto a known humidity prior to moving the paper through the substantiallyvertical nip. This can be achieved by moving the paper to a room withcontrolled ambient air humidity and temperature. Further, thesubstantially vertical nip may be at a controlled humidity andtemperature, such that the paper is conditioned and maintained at theknown moisture content.

Alternatively, or additionally, one embodiment of the machinery utilizedfor testing the tendency of a paper to curl is depicted in FIGS. 3 a-b.FIGS. 3 a and 3 b depicts a rapid conditioning system 48 having void 60defined by an solid outer wall, solid side walls 46, and angled innerwall 44. A vacuum pump 50 is connected to the interior of the void 60with tubing through a fitting in one of the sides. The presentembodiment contains a multiplicity of angled inner walls 44 to increasethe speed of the conditioning process. However, a conditioning systemhaving a single inner wall is within the teachings of the invention.

Outer and side walls 42 and 46 are made of any non-permeable substance,for example, plywood, and are further preferably sealed with silicone.Additionally, the thickness of the outer and side walls can varygreatly. For cost efficiency, however, the present embodiment includes athickness of about ¼ of an inch. The angled walls are preferably made ofpermeable substance. In the present embodiment, the angled walls have aback side of perforated plastic sheets that are about ⅛ of an inch thickwith a 50% hole pattern (wherein the material is 50% hole area and 50%plastic), covered by a front side having about ½ inch of open inch cellfoam. The materials and/or thickness of the materials are variable aslong as the material retains a form of permeability.

The method for predicting the tendency of a paper to curl can have papersamples move from the paper making machine to the humidifier to thesubstantially vertical nip in a single automated in-line process. Othermethod embodiments include physically moving the paper samples from oneapparatus to another, or a combination of in-line and physical movement.One preferred embodiment includes the following. Paper samples from apaper making machine are removed from the machine and cut into 8½×8½inch sheets. The sheets are brought to the rapid conditioner system ofFIG. 3 a-3 b. Up to six sheets are placed on the front of the angledsides 44. The vacuum pump is activated, drawing the ambient humidifiedair through the tester sheets and the angles walls, thereby rapidlyconditioning the test sheets to the ambient air humidity, preferablystandard TAPPI conditions of 70° F. and 50% relative humidity. Thehumidity conditioning process lasts for about five minutes, after whichthe vacuum pump is deactivated and the conditioned test samples areremoved. The vacuum may be operably connected to a timer system thatautomatically deactivates the vacuum after five minutes or another settime interval. Alternatively, the vacuum may be deactivated manually. Infurther embodiments, the rapid conditioner system includes a humiditysensor that shuts off the system when a desired humidity is reached inthe paper.

After conditioning, the conditioned test papers are removed from thehumidity conditioning system and further cut into sheets about 4½×4½inches, although the exact size may vary. The temperature in the nip isadjusted by programming the computer to activate the heating lamp,thereby heating the roller 14 within the range of 150-450° F. The springpressure of roller 16 is adjusted to the maximum allowable pressurewherein pressure within the nip is minimal such that there would be nomechanical curl on a paper put through the nip if the rollers were notheated. The newly cut and humidified sheets are manually carried to thecurl tester 10, one embodiment of which is depicted in FIG. 4.

The paper samples are placed into the feed tray 58 of the curl testingunit, which holds the test paper in an substantially vertical, oblongorientation. The feed tray feeds the substantially vertically orientedtest paper between the substantially vertically oriented rollers, whichheat the test paper to 165° F. or another specific desired temperature,preferably within the range of 50-350° depending on the paper grade. Asthe paper exits, the nip laser sensors 26 and 28 emit parallel laserbeams that measure deviation of the paper from the centerline. The twosensor readings are used to calculate the total curl of the paper, thesum of both laser sensor readings, and the diagonal curl of the paper,the absolute difference between the two laser sensor readings. Uponfully exiting the nip, the test papers drop into catch tray 56 for easyremoval.

The simplex curl tendency of a paper is calculated by combining themoisture content of the test paper with the total curl values of thetest paper. In one embodiment, a regression analysis equation used tocalculate tendency to curl isSxMax=325−142*(Moisture)+15.6*(MoistSQ)+0.341 Total Crlwherein Sx Max=the Maximum simplex curl in a targeted xerographicmachine, Moisture=the ambient moisture found in a newly opened ream ofpaper, MoistSQ=the square of the ream moisture, and Crl=the diagonalcurl measured form the curl tester. The equation has an r-square of76.5%.

Other empirically developed equations can be arrived at depending onwhat type of apparatus with which the test papers are meant to be used.In one test, thirty six sample papers were put through the curl testerand diagonal curl was measured, as shown in TABLE 1.

TABLE 1 Actual Maximum Predicted SxMax Ream Moisture, Simplex curl onwith Moisture, Fuser Curl measured (Ream Sample Xerox 5388, FeltMoisture Square Tester ahead of Xerox Moisture) Number Sample Side orWire Side and Fuser Curl Reading 5388 Curl Test Squared 1 20#Benchmarking A1 12.5 14.8 20 5.18 26.8324 2 20# Benchmarking A2 17.514.4 24 5.08 25.8064 3 20# Benchmarking A3 12.5 12.5 28 4.81 23.1361 420# Benchmarking B2 20.0 20.4 43 5.05 25.5025 5 20# Benchmarking B3 15.016.6 30 5.09 25.9081 6 20# Benchmarking C1 22.5 15.3 28 5.05 25.5025 720# Benchmarking C3 17.5 14.5 27 5.02 25.2004 8 20# Benchmarking C5 22.518.8 36 5.1 26.01 9 20# Benchmarking D1 27.5 23.4 27 5.44 29.5936 10 20#Benchmarking D2 27.5 20.3 36 5.18 26.8324 11 20# Benchmarking E1 15.021.3 40 5.16 26.6256 12 20# Benchmarking E2 30.0 18.2 37 5.04 25.4016 1320# Benchmarking W1 20.0 17.1 41 4.84 23.4256 14 20# Benchmarking W225.0 16.5 41 4.75 22.5625 15 20# Benchmarking W3 22.5 18.2 45 4.3 18.4916 24# Benchmark A-1 20.0 9.7 16 4.16 17.3056 17 24# Benchmark B-1 12.513.5 29 4.22 17.8084 18 24# Benchmark C1-30 15.0 15.6 31 4.1 16.81 1924# Benchmark C1-35 15.0 13.2 33 4.62 21.3444 20 24# Benchmark D-1 10.09.8 13 4.08 16.6464 21 24# Benchmark E-1 12.5 10.8 22 4.25 18.0625 2224# Benchmark GP-1 15.0 12.2 27 4.28 18.3184 23 C30 Size Press Trial -20.0 18.9 40 5.02 25.2004 30H15051E 24 C30 Size Press Trial - 17.5 16.132 5.01 25.1001 30H15071E 25 C30 Size Press Trial - 15.0 13.7 33 4.7422.4676 30H15093E 26 C35 Normal Paper 27.5 20.2 32 5.24 27.4576 27Eastover Profile 4L 20.0 17.0 34 5.03 25.3009 28 Eastover Profile A122.5 21.1 54 4.78 22.8484 29 Eastover Profile A2 22.5 17.6 45 4.7122.1841 30 Eastover Profile X7 15.0 2.0 4.64 21.5296 31 Eastover ProfileX8 20.0 19.0 50 4.62 21.3444 32 Eastover Relicopy 10.0 10.5 25 4.6321.4369 33 Ray Clements Box #1 37.5 34.7 42 5.64 31.8096 34 Ray ClementsBox 17 40.0 30.7 46 5.47 29.9209 35 Ray Clements Box 690 30.0 30.1 465.45 29.7025 36 Relizon/Eastover Curl 40.0 38.8 53 5.65 31.9225Complaint

Plotted out in the graph shown in FIG. 5, the predicted simplex curl ofeach sample point except point 30 (missing value) is compared to actualmeasure simplex curl. The resultant standard deviation of the predictedcurl from the actual curl is lower than 5%.

The tendency of a paper to simplex curl can be predicted for standardlaser printers, photocopiers or other like apparatuses. Further,corrective data can be tabulated from the predicted tendency to correctthe tendency of a non-sample paper to curl in a paper making machine.The corrective information is then fed back into a data acquisition orpaper making machine control system. The calculated data can be used tocorrect curl tendency by controlling head box rush/drag ratios and jetprofiles in a paper making machine as known in the art. In otherembodiments, the data can be automatically fed into a paper makingmachine with a feed back loop to the paper making machine.

Although the invention has been described with reference to preferredembodiments, it will be appreciated by one of ordinary skill in the artthat numerous modifications are possible in light of the abovedisclosure. For example, the nip can be any kind of nip known in theart, as long as it is substantially vertically oriented. All suchvariations and modifications are intended to be within the scope andspirit of the invention as defined in the claims appended hereto.

1. A method for measuring the tendency of a paper to achieve simplexcurl, comprising moving a paper sample from a paper making machinethrough a substantially vertical nip positioned such that the papersample exits from the substantially vertical nip in a substantiallyvertical orientation, measuring the total curl of the paper sample as orafter the paper sample exits the substantially vertical nip, andtabulating corrective data to correct the tendency of a non-sample paperto curl in the paper making machine based.
 2. The method according toclaim 1, further comprising maintaining the substantially vertical nipand the paper sample at a controlled humidity and temperature, such thatthe paper is conditioned by the humidity and temperature to achieve aknown moisture content.
 3. The method according to claim 1, furthercomprising conditioning the paper sample to a known moisture contentprior to moving the paper sample through the substantially vertical nip.4. The method according to claim 1, further comprising feeding thecorrective data into a data acquisition or paper making machine controlsystem.
 5. The method according to claim 1, wherein the measuring isperformed using a curl measuring device comprising a multiplicity oflasers directed at the paper sample.
 6. The method according to claim 1,wherein the substantially vertical nip is heated.
 7. The methodaccording to claim 1, wherein the substantially vertical nip is heatedto a minimum temperature of 150° F.
 8. The method according to claim 1,wherein the substantially vertical nip is heated to a maximumtemperature of 450° F.
 9. An apparatus for performing a method formeasuring the tendency of a paper to achieve simplex curl, the methodcomprising moving a paper sample from a paper making machine through asubstantially vertical nip positioned such that the paper sample exitsfrom the substantially vertical nip in a substantially verticalorientation and predicting the tendency of a paper to curl with aregression analysis equation that accounts for the moisture content ofthe paper sample and the total curl of the paper sample, the apparatuscomprising a rotatable first roller, wherein the first roller isrotatable around a first substantially vertical axis in a substantiallyvertical plane; a rotatable second roller, wherein the second roller isrotatable around a second substantially vertical axis in thesubstantially vertical plane, the first substantially vertical axisparallel to the second substantially vertical axis, and the first andsecond rollers rotatable in opposing directions; a substantiallyvertical nip point between the first roller and the second roller suchthat a paper or paperboard can pass through the substantially verticalnip point; and a means for predicting tendency of a paper to simplexcurl with a regression analysis equation that accounts for the moisturecontent of the paper sample and the total curl of the paper sample. 10.The apparatus according to claim 9, further comprising means formeasuring a total curl of the paper sample as or after the paper sampleexits the substantially vertical nip.
 11. The apparatus according toclaim 9, further comprising a means for maintaining the substantiallyvertical nip and the paper sample at a controlled humidity andtemperature, such that the paper is conditioned by the humidity andtemperature to achieve a known moisture content.
 12. The apparatusaccording to claim 9, further comprising a means for conditioning thepaper sample to a known moisture content prior to moving the papersample through the substantially vertical nip.
 13. The apparatusaccording to claim 12, further comprising a means for feeding thecorrective data into a data acquisition or paper making machine controlsystem.
 14. An apparatus for performing the method according to claim 1,comprising a rotatable first roller, wherein the first roller isrotatable around a first substantially vertical axis in a substantiallyvertical plane; a rotatable second roller, wherein the second roller isrotatable around a second substantially vertical axis in thesubstantially vertical plane, the first substantially vertical axisparallel to the second substantially vertical axis, and the first andsecond rollers rotatable in opposing directions; a substantiallyvertical nip point between the first roller and the second roller suchthat a paper or paperboard can pass through the substantially verticalnip point; a measuring means for measuring a total curl of the paper orpaperboard; and a means for tabulating corrective data to correct thetendency of a non-sample paper to curl in the paper making machine. 15.The apparatus according to claim 14, further comprising a means formaintaining the substantially vertical nip and the paper sample at acontrolled humidity and temperature, such that the paper is conditionedby the humidity and temperature to achieve a known moisture content. 16.The apparatus according to claim 14, further comprising a means forconditioning the paper sample to a known moisture content prior tomoving the paper sample through the substantially vertical nip.
 17. Theapparatus according to claim 14, further comprising a means for feedingthe corrective data into a data acquisition or paper making machinecontrol system.
 18. The apparatus according to claim 14, wherein themeasuring means is a curl measuring device comprising a multiplicity oflasers directed at the paper sample.